Method of measuring taper angle in wire electric discharge machining apparatus and measuring tool

ABSTRACT

A method of measuring a taper angle in a wire electric discharge machining apparatus comprises, the steps of: providing a measuring tool ( 2 ) having lower and upper edges ( 27, 23 ) being spaced by a given height (H); moving a vertical wire electrode (EV) from a reference position (R) in one direction by a first movement (X 1 ) to the lower edge ( 27 ); moving the vertical wire electrode from the reference position in the one direction by a second movement (X 2 ) to the upper edge ( 23 ); moving an inclined wire electrode (EI) from the reference position in the one direction by a third movement (X 3 ) to the lower edge; moving the inclined wire electrode from the reference position in the one direction by a fourth movement (X 4 ) to the upper edge; and calculating a taper angle (θ) of the inclined wire electrode based on the following equation: 
       θ=tan −1   γ/H    
       γ=|( X   3   −X   1 )−( X   4   −X   2 )|

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wire electric discharge machiningapparatus in which a wire electrode is vertically supported undertension between upper and lower wire guides. In particular, the presentinvention relates to a method of measuring a taper angle of the wireelectrode.

2. Description of the Related Art

A wire electric discharge machining apparatus is widely known which cutsa plate-like workpiece in a manner analogous to a band saw by supplyinga series of current pulses to a moving wire electrode. Taper cut isknown as cutting using a wire electrode which is inclined by aninstructed taper angle by moving one of the wire guides relative to theother in a horizontal XY plane.

Japanese Laid-open utility model application 3-103119 discloses a methodof measuring a taper angle of wire electrode with a measuring tool. Asillustrated in FIG. 1A, a measuring tool 1 is conventionally used tomeasure a taper angle of wire electrode. The measuring tool 1 is made ofconductive material and includes a rectangular body 10 and two parallelarms 12 and 16. The arms 12 and 16 extend longitudinally from one sideof the rectangular body 10 and have respective sharp edges 13 and 17.The sharp edges 13 and 17 extend longitudinally and parallel and arevertically spaced by a given height H. The bottom of the measuring tool1 includes the lower edge 17. The upper and lower sharp edges 13 and 17are laterally spaced and face each other.

A conventional method of measuring a taper angle will now be describedwith reference to FIGS. 1A and 1B.

The measuring tool 1 is positioned on an XY table T so that the edges 13and 17 extend in the direction of Y-axis. The XY table T is moveable inthe directions of orthogonal X and Y axes. A wire electrode can be movedwithin an XY plane relative to the measuring tool 1 by movement of theXY table T.

A wire electrode is aligned vertically to an XY plane between upper andlower wire guides GU and GL. The upper wire guide GU is moveable in thedirections of orthogonal U and V axes. The U-axis is parallel to theX-axis and the V-axis is parallel to the Y-axis. The vertical wireelectrode is positioned at a reference position R between the sharpedges 13 and 17 by movement of the XY table T. Coordinates (x, y) of thereference position R are stored.

The vertical wire electrode EV is moved in a negative X-axis direction.At step S1, when electrical contact between the wire electrode EV andthe upper sharp edge 13 is detected, the XY table T is stopped and afirst X-axis movement X1 is stored. The wire electrode EV is returned tothe reference position R.

The wire electrode EV is moved in a positive X-axis direction. At stepS2, when electrical contact between the wire electrode EV and the lowersharp edge 17 is detected, the XY table T is stopped and a second X-axismovement X2 is stored. The wire electrode EV is returned to thereference position R.

The wire electrode is inclined at an instructed taper angle θ by movingthe upper wire guide GU in a positive U-axis direction. A U-axismovement U of the upper wire guide GU is stored.

The inclined wire electrode EI is moved in a negative X-axis direction.At step S3, when electrical contact between the wire electrode EI andthe upper sharp edge 13 is detected, the XY table T is stopped and athird X-axis movement X3 is stored. The wire electrode EV is returned tothe reference position R.

The wire electrode EI is moved in a positive X-axis direction. At stepS4, when electrical contact between the wire electrode EI and the lowersharp edge 17 is detected, the XY table T is stopped and a fourth X-axismovement X4 is stored.

A taper angle θ is expressed by an equation (1):

θ=tan⁻¹ γ/H   (1)

γ is expressed by an equation (2):

γ=α−β  (2)

α and β are expressed by equations (3) and (4), respectively:

α=|(X3+R/cosθ)−(X1+R)|  (3)

β=|(X2+R)−(X4+R/cosθ)|  (4)

R is a radius of wire electrode. Based on the equations (2), (3) and(4), γ is expressed by an equation (5):

γ=(↑X3|+|X4|)−(|X1|+∥X2∥)+2R(1/cosθ−1)   (5)

The value γ may be inaccurate as the equation (5) includes taper angle θof which actual value has not been obtained. SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of accuratelymeasuring a taper angle of wire electrode.

Another object of the present invention is to provide a measuring toolfor accurately measuring a taper angle of wire electrode.

According to one aspect of the present invention, a method of measuringa taper angle in a wire electric discharge machining apparatuscomprises, the steps of:

(a) providing a measuring tool (2) having lower and upper edges (27, 23)being spaced by a given height (H);

(b) aligning a wire electrode vertically between a pair of wire guides(GL, GU);

(c) moving the vertical wire electrode (EV) from a reference position(R) in one direction by a first movement (X1) until contact between thewire electrode and the lower edge (27) is detected;

(d) moving the vertical wire electrode from the reference position inthe one direction by a second movement (X2) until contact between thewire electrode and the upper edge (23) is detected;

(e) inclining the wire electrode at a taper angle (θ);

(f) moving the inclined wire electrode (EI) from the reference positionin the one direction by a third movement (X3) until contact between thewire electrode and the lower edge is detected;

(g) moving the inclined wire electrode from the reference position inthe one direction by a fourth movement (X4) until contact between thewire electrode and the upper edge is detected; and

(h) calculating the taper angle based on the first, second, third andfourth movements and the given height.

The taper angle θ may be calculated by the following equation:

θ=tan⁻¹ γ/H

γ=|(X3−X1)−(X4−X2)|

According to another aspect of the present invention, a measuring toolfor measuring a taper angle in a wire electric discharge machiningapparatus comprises:

a rectangular body (20);

a lower arm (26) extending from one side of the rectangular body, havinga lower sharp edge (27);

an upper arm (22) extending from one side of the rectangular body andhaving an upper sharp edge (23); and

wherein the upper and lower sharp edges face the same direction.

Preferably, the upper arm is longer than the lower arm.

It is preferable that the upper and lower sharp edges extend paralleland longitudinally and are vertically and laterally spaced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view illustrating a conventional measuringtool.

FIG. 1B illustrates a conventional method of measuring a taper angle ofwire electrode with the measuring tool of FIG. 1A.

FIG. 2A is a perspective view illustrating a measuring tool of thepresent invention.

FIG. 2B illustrates a method of measuring a taper angle of wireelectrode with the measuring tool of FIG. 2A according to the presentinvention.

PREFERRED EMBODIMENT OF THE INVENTION

A method of measuring a taper angle of wire electrode according to thepresent invention will now be described with reference to FIGS. 2A and2B. The similar elements are labeled with similar reference numerals asused in FIGS. 1A and 1B.

As illustrated in FIG. 2A, a measuring tool 2 which is made ofconductive material and includes a rectangular body 20 and two arms 22and 26 is provided. The arms 22 and 26 extend longitudinally from oneside of the rectangular body 20 and have respective sharp edges 23 and27. The arms 22 and 26 have different lengths and widths. In theillustrated embodiment, the upper arm 22 is longer and narrower than thelower arm 26. The sharp edges 23 and 27 extend parallel andlongitudinally of the measuring tool 2. The sharp edges 23 and 27 arevertically spaced by a given height H. The sharp edges 23 and 27 havethe same angle and face the same direction, i.e. a positive X-axisdirection. The sharp edges 23 and 27 are laterally spaced. The bottom ofthe measuring tool 2 includes the lower edge 27.

The measuring tool 2 is positioned on an XY table T so that the edges 23and 27 extend in the direction of Y-axis. A wire electrode is alignedvertically to the XY plane between a pair of wire guides GU and GL. Theupper wire guide GU is moveable in the directions of orthogonal U and Vaxes. The vertical wire electrode is positioned at a reference positionR so as to face the lower sharp edge 27. Coordinates (x, y) of thereference position R are stored.

The vertical wire electrode EV is moved in a negative X-axis directionby a first X-axis movement X1 until electrical contact between the wireelectrode EV and the lower sharp edge 27 is detected, at step S1. Thefirst X-axis movement X1 is stored and the wire electrode EV is returnedto the reference position R.

The wire electrode EV is slightly moved in a negative Y-axis directionso as to face the upper sharp edge 23. The wire electrode EV is furthermoved in a negative X-axis direction by a second X-axis movement X2until electrical contact between the wire electrode EV and the uppersharp edge 23 is detected, at step S2. The second X-axis movement X2 isstored and the wire electrode EV is returned to the reference positionR.

The wire electrode is inclined at an instructed taper angle θ by movingthe upper wire guide GU in a positive U-axis direction. A U-axismovement U of the upper wire guide GU is stored.

The inclined wire electrode EI is moved in a negative X-axis directionby a third X-axis movement X3 until electrical contact between the wireelectrode EI and the lower sharp edge 27 is detected, at step S3. Thethird X-axis movement X3 is stored and the wire electrode EV is returnedto the reference position R.

The wire electrode EI is slightly moved in a negative Y-axis directionso as to face the upper sharp edge 23. The wire electrode EI is furthermoved in a negative X-axis direction by a fourth X-axis movement X4,until electrical contact between the wire electrode EI and the uppersharp edge 23 is detected, at step S4. The fourth X-axis movement X4 isstored.

α and β in FIG. 2B are expressed by equations (6) and (7), respectively:

α=|(X3+R/cosθ)−(X1+R)|  (6)

β=|(X4+R/cosθ)−(X2+R)|  (7)

Based on the equations (2), (6) and (7), γ is expressed by an equation(8):

65 =|(X3−X1)−(X4−X2)|  (8)

Taper angle θ can be accurately calculated on the equation (1) as theequation (8) includes only measured values X1, X2, X3 and X4.

It is essential to accurately set a distance TL between the table T anda turning point in the lower wire guide GL and a distance TU between thetable T and another turning point in the upper wire guide GU. Thoseturning points, where the taper angle of wire electrode is actuallyformed, deviate from nominal values depending on the taper angle θ. TLand TU can be calculated by equations (9) and (10), respectively:

TL=α×γ/H   (9)

TU=(U−α)×γ/H   (10)

The present invention is not intended to be limited to the disclosedform. It is clear that many improvements and variations are possiblewith reference to the above description. The illustrated embodiment wasselected to explain the essence and practical application of theinvention. The scope of the invention is defined by the attached claims.

1. A method of measuring a taper angle in a wire electric dischargemachining apparatus comprising, the steps of: (a) providing a measuringtool having lower and upper edges being spaced by a given height; (b)aligning a wire electrode vertically between a pair of wire guides; (c)moving the vertical wire electrode from a reference position in onedirection by a first movement until contact between the wire electrodeand the lower edge is detected; (d) moving the vertical wire electrodefrom the reference position in the one direction by a second movementuntil contact between the wire electrode and the upper edge is detected;(e) inclining the wire electrode at a taper angle; (f) moving theinclined wire electrode from the reference position in the one directionby a third movement until contact between the wire electrode and thelower edge is detected; (g) moving the inclined wire electrode from thereference position in the one direction by a fourth movement untilcontact between the wire electrode and the upper edge is detected; and(h) calculating the taper angle based on the first, second, third andfourth movements and the given height.
 2. The method of claim 1, whereinthe step (h) includes calculating the taper angle 0 by the followingequation:θ=tan⁻¹ γ/Hγ=|(X3−X1)−(X4−X2)| wherein H represents the given height and X1, X2, X3and X4 represent the first, second, third and fourth movements,respectively.
 3. A measuring tool for measuring a taper angle in a wireelectric discharge machining apparatus comprising: a rectangular body; alower arm extending from one side of the rectangular body, having alower sharp edge; and an upper arm extending from one side of therectangular body and having an upper sharp edge; wherein the upper andlower sharp edges face the same direction.
 4. The measuring tool ofclaim 3, wherein one of the upper and lower arms is longer than theother.
 5. The measuring tool of claim 3, wherein the upper arm is longerthan the lower arm.
 6. The measuring tool of claim 3, wherein the upperand lower sharp edges extend parallel.
 7. The measuring tool of claim 3,wherein the upper and lower sharp edges extend longitudinally and arevertically and laterally spaced.
 8. The measuring tool of claim 3,wherein the upper and lower sharp edges have the same angle.
 9. Themeasuring tool of claim 3, wherein the bottom of the measuring toolincludes the lower sharp edge.